National list MP Paul Foster-Bell is defending a huge spike in his taxpayer-funded expenses as he campaigned for a seat selection.

Wellington-based Foster-Bell's spending increased from $7459 between July and September last year to $14, 224 in the following October to December quarter. Between January and March, he claimed $12,732. He has claimed almost $35,000 in travel expenses in just over a year.

Foster-Bell sought selection in Whangarei but lost to Dr Shane Reti. But Foster-Bell says he was not using public cash for political campaigning, and all his spending is within the rules. "I am adamant that I am not just squeaky clean but 110 per cent squeaky clean," he insisted.

The former diplomat says he pays out of his own pocket for any personal travel, or for party political business. However, he admits he could have carried out campaigning for the seat while he was in Whangarei on official parliamentary business. He grew up in the town but now lives on the Terrace, Wellington, a short walk from Parliament.

"While I was up there [Whangarei] I travelled there to do official business with a parliamentary purpose, and whether I might have done another thing, or two, in the afternoon - that could well be the case."

He could not say how often this occurred.

As a back-bench MP, Foster-Bell is paid around $150,000 a year.

MPs are entitled to free domestic flights across the country, which is considered part of their salary package. Rental car hire, accommodation and taxi charges are only allowed for parliamentary business, and a Parliamentary Service guide underlining the rules for the election was issued to MPs last month.

Foster-Bell says he did "a huge amount of travel" to the provinces and travels often for commercial visits, and select committee meetings. The trips included a visit to the court and district health board in Whangarei and attending Dargaville field days. He's also been to Timaru to open a salmon farm and represented Prime Minister John Key in Dunedin. "I think if you are not travelling at all you are not being an active MP, and you are not doing your job."

Foster-Bell is standing in Wellington Central, which he unsuccessfully contested in 2011. Ranked 56th on the party list, he was called to Parliament last May to replace Jackie Blue.

Last week National list MP Claudette Hauiti announced she was quitting politics at the election after surrendering her parliamentary charge card for unauthorised spending.

"I know with Claudette you think there is a wider issue here, but from my own point of view if there is any implication that I was less than proper with my expenses, I would reject that 100 per cent."

Taxpayers Union executive director Jordan Williams says MPs' expense claims should be open to scrutiny, as with ministers and government departments' chief executives. "The public pay for it, so the public should be entitled to know."